CN112994690A - Time-to-digital converter and conversion method - Google Patents

Time-to-digital converter and conversion method Download PDF

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CN112994690A
CN112994690A CN202011405155.5A CN202011405155A CN112994690A CN 112994690 A CN112994690 A CN 112994690A CN 202011405155 A CN202011405155 A CN 202011405155A CN 112994690 A CN112994690 A CN 112994690A
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time
locked loop
edge position
digital converter
input signal
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CN112994690B (en
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吴靖大
李羲显
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Hyundai Mobis Co Ltd
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Hyundai Mobis Co Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/081—Details of the phase-locked loop provided with an additional controlled phase shifter
    • H03L7/0812—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used
    • H03L7/0818—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used the controlled phase shifter comprising coarse and fine delay or phase-shifting means
    • G—PHYSICS
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F10/00—Apparatus for measuring unknown time intervals by electric means
    • G04F10/005—Time-to-digital converters [TDC]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
    • H03L7/22—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using more than one loop
    • H03L7/23—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using more than one loop with pulse counters or frequency dividers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S17/14—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4912—Receivers
    • G01S7/4915—Time delay measurement, e.g. operational details for pixel components; Phase measurement
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/0805—Details of the phase-locked loop the loop being adapted to provide an additional control signal for use outside the loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/089—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/091—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector using a sampling device
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/093—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
    • H03M1/0602—Continuously compensating for, or preventing, undesired influence of physical parameters of deviations from the desired transfer characteristic
    • H03M1/0604—Continuously compensating for, or preventing, undesired influence of physical parameters of deviations from the desired transfer characteristic at one point, i.e. by adjusting a single reference value, e.g. bias or gain error

Abstract

The invention relates to a time-to-digital converter and a conversion method, the time-to-digital converter according to an embodiment of the invention comprises: a phase-locked loop section multiplying an input reference clock by using the phase-locked loop; a counting unit that counts the multiplied reference clock and records an edge position of an input signal; a delay locked loop section decomposing the multiplied reference clock into multiphase clocks using a delay locked loop, and sensing an edge position portion of the recorded input signal in the decomposed multiphase clocks to record a fine edge position; and a control section calculating a time difference of a flight time between a start signal and a stop signal of the input signal using the recorded edge position and the recorded fine edge position.

Description

Time-to-digital converter and conversion method
Technical Field
The present invention relates to a time-to-digital converter and a conversion method, and relates to a time-to-digital converter and a conversion method that can be used in a laser radar system, for example.
Background
Laser radar (LIDAR) is a technology for measuring distance by detecting an object using Light. The laser radar measures physical properties such as distance, concentration, speed and shape of an object to be measured by using time, intensity, frequency change, polarization state change and the like of scattering or reflecting after laser is emitted.
The lidar is similar to a RaDAR (RaDAR) that finds a distance by using a round trip time until an ultrahigh frequency is observed to a target object, but is different in that the lidar uses light And the RaDAR uses Radio waves, And the lidar is also called a "video RaDAR".
A Time-to-Digital Converter (TDC) used in a lidar system or the like is a device that recognizes events and provides a Digital representation of the Time at which the event occurred or measures the Time interval between 2 events.
The conventional time-to-digital converter has a Vernier inverter (Vernier inverter) structure. In the vernier inverter structure, inverters are connected in series, and the delay accuracy of each inverter means the time resolution. The conventional time-to-digital converter determines a delay difference at a rising edge of the start signal and the stop signal. After the rising edge of the start signal time point, the internal counter value of the time at which the object returns is activated at the stop signal time point, the number of counters from the start signal to the stop signal being converted into the actual distance. As described above, the series inverter chain becomes resolution.
A problem with the existing approach is that existing time-to-digital converters use only a single channel. In addition, the existing time-to-digital converters have a high dependency on inverter delay. The detectable time range of existing time-to-digital converters is narrow. The counter value from the time point of the start signal to the time point of the stop signal is the measurable distance. Since the existing time-to-digital converter depends on the change of the external environment, it is difficult to have a stable high resolution.
As described above, the conventional time-to-digital converter used in the laser radar system uses only a single channel, has a high dependency on inverter delay, has a narrow detectable time range, and depends on a change in external environment, and thus has a problem that it is difficult to have a stable high resolution.
Disclosure of Invention
Technical problem to be solved
An embodiment of the present invention has an object to provide a time-to-digital converter and a conversion method that can accurately measure a distance by outputting a time difference between a start signal and a stop signal, which are input using a phase-locked loop and a delay-locked loop together, as a digital value.
However, the problem to be solved by the present invention is not limited thereto, and various extensions may be made in the environment within the scope not departing from the spirit and field of the present invention.
Means for solving the problems
A time-to-digital converter according to an embodiment of the present invention includes: a Phase-Locked Loop section that multiplies an input reference clock by a Phase-Locked Loop (PLL); a counting part for counting the frequency-multiplied reference clock and recording the edge position of the input signal; a Delay Locked Loop part decomposing the multiplied reference clock into a multiphase clock using a Delay Locked Loop (DLL), and recording a fine edge position by sensing an edge position part of the recorded input signal in the decomposed multiphase clock; and a control section that calculates a Time difference of a Time of Flight (ToF, Time of Flight) between a start signal and a stop signal of the input signal using the recorded edge position and the recorded fine edge position.
The edge position and the fine edge position may be recorded at each of a Rising edge (Rising edge) and a Falling edge (Falling edge) of the input signal.
In addition, the delay locked loop part may include: a first dll section for decomposing the multiplied reference clock into a first multiphase clock by using a first dll; and a second dll section for decomposing the decomposed first multiphase clock into a second multiphase clock by using a second dll.
In an embodiment, the delay locked loop section senses an edge position portion of the recorded input signal in the decomposed multi-phase clock to record a first fine edge position and senses the recorded first fine edge position portion in the decomposed second multi-phase clock to record a second fine edge position.
In addition, when the input signal is a multichannel input signal, the control unit may expand a channel of a stop signal of the input signal.
The control unit may check the signal intensity of the input signal, distinguish an object using the checked signal intensity, and correct a distance error from the object using the checked signal intensity.
In addition, when the light transmitted to the target object is reflected by the object, the control part may remove noise information corresponding to the reflected light using the pulse width and the conversion time information.
The time-to-digital conversion method in the laser radar system according to an embodiment of the present invention includes: a step of decomposing the multiplied reference clock into multiphase clocks using a Delay Locked Loop (DLL); counting the frequency-multiplied reference clock and recording the edge position of the input signal; a step of sensing the edge position portion of the input signal in the decomposed multiphase clock and recording a fine edge position; and calculating a Time difference in Time of Flight (ToF, Time of Flight) between a start signal and a stop signal of the input signal using the edge positions and the fine edge positions.
The edge position and the fine edge position may be recorded at each of a Rising edge (Rising edge) and a Falling edge (Falling edge) of the input signal.
In one embodiment, the step of recording the fine edge positions may include the step of decomposing the multiplied reference clock into a first multi-phase clock using a first delay locked loop; and a step of decomposing the decomposed first multiphase clock into a second multiphase clock using a second delay locked loop.
In one embodiment, the step of recording the fine edge positions may record a first fine edge position by sensing an edge position portion of the recorded input signal in the divided multiphase clock, and may record a second fine edge position by sensing the recorded first fine edge position portion in the divided second multiphase clock.
In the step of calculating the time-of-flight difference, it is possible to confirm the signal intensity of the input signal, distinguish a target object using the confirmed signal intensity, and correct a distance error from a target object using the confirmed signal intensity.
In addition, in the step of calculating the time-of-flight difference, when the light transmitted to the target object is reflected by the object, noise information corresponding to the reflected light may be removed using the pulse width and the conversion time information.
Effects of the invention
The disclosed technology may have the following effects. However, this does not mean that the specific embodiment should include all or only the following effects, and thus, it should not be understood that the scope of the claims of the disclosed technology is limited thereto.
Embodiments of the present invention may utilize multiple phases to design a high resolution time-to-digital converter.
Embodiments of the present invention can exhibit robust characteristics to an external environment by using a phase locked loop and a delay locked loop as a feedback system. For example, the external environment may include variations in temperature and supply voltage, variations in manufacturing processes, and the like.
Embodiments of the present invention can easily extend a channel with a small area by constituting a delay locked loop by the channel.
Embodiments of the present invention may use a counter to improve the sensing capability of a distant signal with the same resolution.
Embodiments of the present invention may improve accuracy by sensing the rising and falling edges of the pulse.
Drawings
Fig. 1 is a diagram showing a configuration of a laser radar system to which an embodiment of the present invention is applied.
Fig. 2 is a diagram illustrating an operation principle of a time-to-digital converter in a laser radar system according to an embodiment of the present invention.
Fig. 3 is a diagram showing a detailed block structure of a time-to-digital converter in the lidar system according to an embodiment of the present invention.
Fig. 4 is a block diagram showing the structure of a time-to-digital converter in the laser radar system according to an embodiment of the present invention.
Fig. 5 is a diagram illustrating an operation timing diagram of a time-to-digital converter according to an embodiment of the present invention.
Fig. 6 and 7 are diagrams illustrating a three-step TDC operation timing of the time-to-digital converter according to an embodiment of the present invention.
Fig. 8 is a diagram showing noise generated in the laser radar system.
Fig. 9 is a diagram showing the transition time of a signal.
Fig. 10 is a diagram showing a pulse width calculation operation using rising edge and falling edge time information.
Fig. 11 is a diagram illustrating an operation of storing edge information of a pulse that enters in a time of detecting distance information.
Fig. 12 is a diagram illustrating an operation of sampling a signal entering a rising edge of a sampling clock with a falling edge.
Fig. 13 is a flowchart illustrating a time-to-digital conversion method in a lidar system according to an embodiment of the present invention.
100: lidar system, 110: emission portion, 120: reception unit, 130: time-to-digital conversion section, 140: MCU section, 200: time-to-digital converter, 210: phase-locked loop portion, 220: counting unit, 230: delay locked loop, 231: first delay locked loop, 232: second delay locked loop, 240: control unit
Detailed Description
Since the present invention can be modified in various ways and can have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail.
However, these specific examples are not intended to limit the present invention to specific embodiments, but should be construed to include all modifications, equivalents, and alternatives included in the spirit and technical scope of the present invention.
The terms first, second, etc. may be used to describe various elements, however, the elements are not limited by the terms. The term is used only for the purpose of distinguishing one constituent element from other constituent elements. For example, a first component may be named a second component, and similarly, a second component may also be named a first component, without departing from the scope of the present invention. The term "and/or" includes a combination of a plurality of related items or one of a plurality of related items.
When a certain component is referred to as being "connected" or "connected" to another component, it may be directly connected or directly connected to another component, but it is to be understood that another component may be present therebetween. In contrast, when a component is referred to as being "directly connected" or "directly connected" to another component, it is to be understood that no other component is present therebetween.
The terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Where no other meaning is explicitly stated in the context, singular expressions include plural expressions. In the present application, terms such as "including" or "having" are to be understood as specifying the presence of the features, numbers, steps, actions, constituent elements, components, or combinations thereof described in the specification, and not excluding the presence or addition possibility of one or more other features, numbers, steps, actions, constituent elements, components, or combinations thereof in advance.
Unless defined otherwise, all terms used herein including technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The same terms as those defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings provided in context of the related art, and should not be interpreted in an ideal or excessive formal sense when not explicitly defined in this application.
Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, for the sake of convenience of understanding as a whole, the same reference numerals are given to the same components in the drawings, and redundant description of the same components is omitted.
Fig. 1 is a diagram showing a configuration of a laser radar system to which an embodiment of the present invention is applied.
A lidar system to which an embodiment of the present invention is applied utilizes a lidar sensor technology used for sensing front and rear objects of an automobile. Lidar systems sense the time of light reflected back by an object to sense distance.
In the automotive field, lidar systems are used to calculate distances to objects. The time difference is calculated and the distance is confirmed by recognizing the start point and the end point by converting the optical signal into an electrical signal. Since the speed of light is the same as the speed of the electric wave, the distance can be obtained by dividing the time the light is reflected back from the object by half and multiplying by the speed of light.
As shown in fig. 1, the laser radar system 100 may be divided into: a transmitting part 110 receiving the electric signal to emit light; a receiving part 120 receiving light and emitting an electrical signal; a time-to-digital conversion part 130 receiving the electric signal and converting time into a digital value; and an MCU unit 140 for monitoring the entire system.
An embodiment of the invention relates to a time-to-digital converter for use in a lidar system. The time-to-digital converter is a circuit that calculates a time difference of an electric signal and outputs it as a digital value. The output digital value is time difference information, and can be converted into distance information when the speed of the electric wave is calculated. An embodiment of the present invention provides a time-to-digital converter of a ranging lidar that can accurately measure a distance.
Fig. 2 is a diagram illustrating an operation principle of a time-to-digital converter in a laser radar system according to an embodiment of the present invention.
An embodiment of the present invention is directed to stably and accurately sensing distance information with respect to a change in an external environment, as a means for solving the problems of the related art. The time-to-digital converter 200 according to an embodiment of the present invention generates a clock signal that generates a stable output against an influence of an external environment using a Phase Locked Loop (PLL) and a Delay Locked Loop (DLL). In addition, the time-to-digital converter 200 can detect a long distance using a counter, and can achieve the same rate accuracy for high resolution using multiple phases. Here, since the phase locked loop and the delay locked loop include the feedback circuit, it is possible to generate a stable output against an external environment such as process variation, temperature, voltage, and the like.
The technical features of the present invention will be explained. It is very important that the time-to-digital converter 200 accurately analyzes the difference between the electric signals and outputs it with high resolution. For example, if a number of bits can be represented for a time of about 100ps, a resolution of 1.5cm is possible.
The time-to-digital converter 200 of the lidar system must process multi-channel time information in a short time and requires high resolution performance with high resolution. Operations and features according to an embodiment of the present invention are as follows.
The time-to-digital converter 200 multiplies the frequency using a Phase Locked Loop (PLL) that receives a reference frequency.
In addition, the time-to-digital converter 200 decomposes the multiplied clock (multiplied clock) into multiple phases (multi-phase) using a Delay Locked Loop (DLL).
The time-to-digital converter 200 counts the multiplied clocks and stores Coarse codes (Coarse codes) for edges of the input signal.
The time-to-digital converter 200 senses a portion in which an edge of an input signal is located in a multi-phase and stores in a fine code (fine code).
The time-to-digital converter 200 calculates the time difference by storing the start signal and the stop signal.
The time-to-digital converter 200 constitutes a system by expanding channels of the stop signal when constituting a multi-channel.
The operation principle of the time-to-digital converter 200 according to an embodiment of the present invention will be described in detail.
The time-to-digital converter 200 multiplies the frequency using a Phase Locked Loop (PLL) that receives a reference frequency. Here, the time-to-digital converter 200 generates a high frequency to improve the overall resolution, and adjusts the duty ratio in order to take into account the rising edge and the falling edge.
In addition, the time-to-digital converter 200 decomposes the multiplied clock into multiple phases using a Delay Locked Loop (DLL). The time-to-digital converter 200 divides the resolution level into a coarse part and a fine part to form one phase.
The time-to-digital converter 200 then counts the multiplied clocks and stores the coarse code at the edges of the input signal. Here, the rising edge and the falling edge are stored separately.
In addition, the time-to-digital converter 200 senses a portion in which an edge of the input signal is located in multiple phases and stores in the fine code. Here, the rising edge and the falling edge are stored separately.
The time-to-digital converter 200 calculates the difference by storing the start signal and the stop signal. Here, the ToF value measured by the rising edge and the ToF value measured by the falling edge are compared, and if it is determined to be a valid signal, the value is applied. On the other hand, when the resolution exceeds a specified value or is abnormal, information is delivered to the user. In addition, since the internal system of the time-to-digital converter 200 knows the resolution of the coarse/fine part, the part where the error occurs can be indirectly known. The time-to-digital converter 200 may accumulate these values, which may be used to correct the value of the incoming signal at a corresponding time thereafter.
On the other hand, when a multichannel is configured, a system can be configured by expanding a stopped channel.
Fig. 3 is a diagram showing a detailed block configuration of a time-to-digital converter in the lidar system according to an embodiment of the present invention.
CLK _25M represents ILFM REFCLK from the TCXO.
ILFM (Injection Locked Frequency Multiplier) represents PLL. The output Frequency (Out Frequency) is 25MHz request ke.
The Counter (Counter) counts ILFM _ out (bold, 13 bits).
The TDC 1CH stores a midamble (Middle code) and a Fine code (Fine code) generated from the ADDLL. Here, the midamble (Middle) is 8 bits, and the Fine code (Fine) is 4 bits, which are stored in the rising edge/falling edge, respectively.
The START (START) signal is a START signal from a pre-driver.
The stop signals 0 to 3 are stop signals from the TIA.
A TDC control unit (TDC Controller) synthesizes the TDC output code and generates a TDC control signal.
Fig. 4 is a block diagram showing the structure of a time-to-digital converter in the laser radar system according to an embodiment of the present invention.
As shown in fig. 4, the time-to-digital converter 200 in the lidar system according to an embodiment of the present invention includes a phase-locked loop 210, a counting unit 220, a delay phase-locked loop 230, and a control unit 240. However, not all of the illustrated components are essential components. The time-to-digital converter 200 may be implemented with more constituent elements than those illustrated, and the time-to-digital converter 200 may also be implemented with fewer constituent elements than those illustrated.
As an example, the time-to-digital converter 200 generates a fast frequency by multiplying the reference clock by 25 times, and stores coefficients for edges of the input pulse using a counter. Here, the coefficient is stored at each rising edge and falling edge (CNT _ Rise/Fall).
The time-to-digital converter 200 divides the fast frequency into 8 phases and records the edge positions of the input pulses. Here, the edge position is recorded at most 3 times per rising edge and falling edge (coarse _ Rise/Fall).
The time-to-digital converter 200 again divides the 8 phases into 4 phases and records the edge positions of the input pulses. Here, the edge position (Fine _ Rise/Fall) is recorded every third rising edge and falling edge.
The time-to-digital converter 200 sums and outputs final data.
Next, a detailed structure and operation of each constituent element of the time-to-digital converter 200 of fig. 4 will be described.
The Phase-Locked Loop section 210 multiplies an input reference clock by a Phase-Locked Loop (PLL).
The counting part 220 counts the reference clock multiplied at the phase-locked loop part 210 and records the Edge (Edge) position of the input signal.
The Delay Locked Loop part 230 decomposes the reference clock multiplied at the phase Locked Loop part 210 into multiphase clocks using a Delay Locked Loop (DLL), senses an edge portion of the input signal recorded at the counting part 220 among the decomposed multiphase clocks, and records a fine edge position.
The control part 240 calculates a Time difference of Time of Flight (ToF, Time of Flight) between the start signal and the stop signal of the input signal using the edge position recorded at the counting part 220 and the fine edge position part recorded at the delay locked loop part 230.
According to an embodiment, the edge positions and the fine edge positions may be recorded for a Rising edge (Rising edge) and a Falling edge (Falling edge) of the input signal, respectively.
According to an embodiment, the delay locked loop part 230 includes: a first dll 231 for decomposing the multiplied reference clock into a first multiphase clock by using a first dll; and a second dll unit 232 for decomposing the decomposed first multi-phase clock into a second multi-phase clock using a second dll.
According to an embodiment, the delay locked loop section 230 may sense an edge position portion of the input signal recorded at the counting section 220 in the divided multi-phase clocks and record a first fine edge position, and may sense the recorded first fine edge position portion in the divided second multi-phase clocks to record a second fine edge position.
According to an embodiment, when the input signal is composed of a multi-channel input signal, the control part 240 may expand a channel of a stop signal of the input signal.
According to the embodiment, the control part 240 confirms the signal intensity of the input signal, can distinguish the target object using the confirmed signal intensity, and can correct the distance error from the target object using the confirmed signal intensity.
According to the embodiment, when the light emitted to the target object is reflected by the object, the control part 240 may remove noise information corresponding to the reflected light using the pulse width and the conversion time information.
In this manner, the time-to-digital converter 200 performs a time-to-digital conversion operation by mixing the phase-locked loop and the delay-locked loop.
The time-to-digital converter 200 performs a high resolution time-to-digital conversion operation by using multiple phases of a delay locked loop.
The time-to-digital converter 200 counts the output of the phase-locked loop, and performs a time-to-digital conversion operation having a wide time domain range.
The time-to-digital converter 200 performs a time-to-digital conversion operation so that high resolution is obtained using the output of the phase locked loop as an input of the delay locked loop.
The time-to-digital converter 200 implements multiple channels to perform time-to-digital conversion operations that improve scalability.
The time-to-digital converter 200 can improve accuracy by sensing the rising and falling edges of the input pulse.
Fig. 5 is a diagram illustrating an operation timing diagram of a time-to-digital converter according to an embodiment of the present invention.
As shown in fig. 5, when the PLL and DLL are in the ready state, the control section 240 outputs soc (start of calibration).
The control part 240 outputs an eoc (end of call) signal after a predetermined time.
Receiving a START (START) signal and a STOP (STOP) signal after the SOC, the control section 240 calculates data for each edge.
The control unit 240 counts the fast frequency (e.g., 625MHz, 1.6ns) and stores a counter value of an edge of an incoming pulse.
In the DLL, rise (rise) information/fall (fall) information of the third input pulse (first from the beginning) is stored per channel.
The control section 240 sums up and outputs final data.
Fig. 6 and 7 are diagrams illustrating a timing of a three-step TDC operation performed by a time-to-digital converter according to an embodiment of the present invention.
As shown in fig. 6 and 7, the time-to-digital converter 200 senses the time between start (Star) and Stop (Stop) through three-Step (Step) time-to-digital conversion (TDC) of Low Power (Low Power) and High Resolution (High Resolution).
The time-to-digital converter 200 senses a Coarse (Coarse) edge through the PLL/counter. In addition, time-to-digital converter 200 senses the second Middle (Middle) edge through C-ADDLL. Time-to-digital converter 200 senses three Fine (Fine) edges through the F-ADDLL.
Fig. 8 is a diagram showing noise generated in the laser radar system.
According to an embodiment of the present invention, noise (walk error) generated in the laser radar system shown in fig. 8 can be improved. In an embodiment of the present invention, when the transition time (transition time) of the input signal is long and the position of the edge cannot be accurately determined, the correction may be performed using the intermediate value of the rising data and the falling data as data.
In addition, a distance detection error signal processing method of the laser radar system will be explained.
Fig. 9 is a diagram showing the transition time of a signal.
Time data of the TOF of the lidar at the output edges of the signal amplifier and the TDC.
In a general laser radar, the rise/fall and Pulse width (Pulse width) of a received signal may be different depending on the distance and the degree of reflection.
The time-to-digital converter 200 according to an embodiment of the present invention can recognize the intensity of the signal to distinguish object information and correct a distance error.
The time-to-digital converter 200 amplifies a signal based on a specific critical point at a signal amplification end. The time-to-digital converter 200 extracts time information by changing the critical point voltage for the same signal. By comparing the difference between the two time information, the transition time of the signal can be known. The time-to-digital converter 200 senses the strength of the signal using the conversion information.
The signal transitions faster when the light is strong and slower when the light is weak. The light intensity at the same distance can be used to determine the state of the object. For example, it can be used to distinguish between white and black boundaries where light is reflected to different degrees. The road surface in front of the moving vehicle has white and black lanes. Even with the same distance information, since the reflection degree is different, it is possible to distinguish lanes while detecting the distance.
In addition, for example, a vehicle made of metal and a person wearing clothes have different light reflectances. Therefore, when a danger is sensed, if a vehicle and a person are distinguished and judged, personal accidents can be avoided.
Fig. 10 is a diagram showing a pulse width calculation operation using rising edge and falling edge time information.
The time-to-digital converter 200 may calculate the pulse width using the time information of the rising and falling edges.
The intensity of the returned light will vary depending on the distance and the pulse width will also vary. The time-to-digital converter 200 may correct an error of the distance information using the pulse width information. The time-to-digital converter 200 may compare the received pulse width information with a look-up table (lookup table) created in advance and use it for final distance information correction.
Fig. 11 is a diagram illustrating an operation of storing edge information of a pulse that enters in a time of detecting distance information.
In practice, light is also reflected by objects such as dust, snow, rain, and the like. A method of distinguishing real objects from noise in such a noisy situation is proposed.
The time when the laser radar detects the distance information is the time when light is emitted to and returned from the LD. In order to detect a distance of 200m, it must be possible to detect a time period of about 1.5 μ s.
The TOF pulse input during a time of 1.5 μ s contains information on objects and information on noise.
If the time information is stored only once, when the noise object is closer than the real object, a problem occurs in that the distance to the real object cannot be determined.
To solve the problem, the time-to-digital converter 200 may store all edge information of the incoming pulse within the distance information detection time and remove noise using the pulse width and conversion time information.
Fig. 12 is a diagram illustrating an operation of sampling a signal entering a rising edge of a sampling clock with a falling edge.
In the lidar system, the edges of TOF pulses are input as asynchronous (Asynchrono μ s) signals, independent of the internal sampling clock.
The TDC using a counter uses a sampling clock having a predetermined period, but a TOF pulse input at a sampling timing edge may not output an accurate counter result.
This can result in a counter 1bit error (counter 1bit error) and errors of more than 20cm can occur when the lidar senses range.
Embodiments of the present invention utilize a method of Retiming (Retiming) an input pulse in a TDC using multiple phases using a DLL.
The time-to-digital converter 200 samples the signal entering the rising edge of the sampling clock with the falling edge while retiming the input pulse with the sampling clock.
For example, as shown in FIG. 12, the red position 301 must have a value of 3/8 or 4/1.
The identified counter value is 3 and the identified multi-phase value is 1, the result is 3/1.
Conversely, a result of 4/8 is also possible.
According to the time-to-digital converter 200 of an embodiment of the present invention, when an input edge enters a position of ' 1 ' or ' phase of 8-phase multiphase, a counter value is stored with a falling of a sampling clock (sampling clock). Then, if the value is 'yes', the counter value is maintained, and if the value is 'yes', the time-to-digital converter 200 stores the value subtracted from the counter value by 1.
The distance detection error can be solved by using a method of preventing such a metastable sampling (metastability sampling) error.
Fig. 13 is a flowchart illustrating a time-to-digital conversion method in a lidar system according to an embodiment of the present invention.
In step S101, the time-to-digital converter 200 multiplies the input reference clock by a Phase Locked Loop (PLL).
In step S102, the time-to-digital converter 200 decomposes the reference clock multiplied at the phase Locked Loop section 210 into multiphase clocks using a Delay Locked Loop (DLL).
In step S103, the time-to-digital converter 200 counts the reference clock multiplied at the phase-locked loop section 210 and records the edge position of the input signal.
In step S104, the time-to-digital converter 200 senses the edge position portion of the input signal recorded at the counting section 220 in the decomposed multiphase clock, and records the fine edge position.
In step S105, the Time-to-digital converter 200 calculates a Time difference of Time-of-Flight (ToF, Time of Flight) between the start signal and the stop signal of the input signal using the edge position recorded at the counting part 220 and the fine edge position recorded at the delay locked loop part 230.
In addition, an embodiment of the present invention may provide a time-to-digital converter 200 and method that utilize multiple phases and high resolution. For example, the time-to-digital converter 200 has a high resolution performance of 50ps, and may have a high precision distance sensing performance of 0.75 cm.
The Phase Locked Loops (PLLs) and Delay Locked Loops (DLLs) utilized in one embodiment of the present invention are feedback systems that exhibit robust characteristics to the external environment. Here, the external environment may include variations in temperature and power supply voltage, variations in manufacturing process, and the like.
The time-to-digital converter 200 according to an embodiment of the present invention commonly uses a Phase Locked Loop (PLL) to constitute a Delay Locked Loop (DLL) from channels, thereby easily expanding the channels with a small area. This can reduce system cost.
The time-to-digital converter 200 according to an embodiment of the present invention can improve sensing capability for a long-distance signal with the same resolution using a counter. For example, about 1.62 e.g., a distance of about 246m may be detected. By dividing the measurement range into two coarse/fine ranges, it is not necessary to increase the counter value more to measure the long distance of the vehicle moving more than 50m per second.
The time-to-digital converter 200 according to an embodiment of the present invention can improve accuracy by sensing the rising and falling edges of the pulse. Noise (wandering error) generated in the laser radar system can be improved. When the transition time of the input signal is long and the position of the edge cannot be accurately determined, the correction may be performed using an intermediate value between rising data and falling data as data.
The above method of the present invention can be implemented by computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording media storing data that can be decoded by a computer system. For example, there may be Read Only Memory (ROM), Random Access Memory (RAM), magnetic tape, magnetic disk, flash Memory, optical data storage devices, and the like.
While the present invention has been described with reference to the drawings and the embodiments, the scope of the present invention is not limited to the drawings and the embodiments, and it should be understood that various modifications and changes can be made by those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention described in the claims.

Claims (13)

1. A time-to-digital converter, comprising:
a phase-locked loop section for multiplying the frequency of the input reference clock by the phase-locked loop;
a counting part for counting the frequency-multiplied reference clock and recording the edge position of the input signal;
a delay locked loop part decomposing the multiplied reference clock into multiphase clocks using a delay locked loop, and recording fine edge positions by sensing edge position portions of the recorded input signal in the decomposed multiphase clocks; and
a control section calculating a time difference of a flight time between a start signal and a stop signal of the input signal using the recorded edge position and the recorded fine edge position.
2. A time-to-digital converter as claimed in claim 1, wherein the edge positions and the fine edge positions are recorded on each of a rising edge and a falling edge of the input signal.
3. The time-to-digital converter of claim 1, wherein the delay locked loop section comprises:
a first delay locked loop part which decomposes the frequency-multiplied reference clock into a first multiphase clock by using a first delay locked loop; and
a second delay locked loop part decomposing the decomposed first multiphase clock into a second multiphase clock using a second delay locked loop.
4. The time-to-digital converter of claim 1, wherein the delay locked loop section senses a recorded edge position portion of the input signal in the decomposed multiphase clock to record a first fine edge position and senses a recorded first fine edge position portion in the decomposed second multiphase clock to record a second fine edge position.
5. The time-to-digital converter of claim 1, wherein the control section expands a channel of a stop signal of the input signal when the input signal is composed of a multi-channel input signal.
6. The time-to-digital converter of claim 1, wherein the control part confirms a signal intensity of the input signal, distinguishes an object using the confirmed signal intensity, and corrects a distance error from the object using the confirmed signal intensity.
7. The time-to-digital converter of claim 1, wherein the control section removes noise information corresponding to the reflected light using a pulse width and conversion time information when the light transmitted to the target object is reflected by the object.
8. A method of time-to-digital conversion in a lidar system, comprising:
a step of multiplying the frequency of an input reference clock by using a phase-locked loop;
a step of decomposing the multiplied reference clock into multiphase clocks using a delay locked loop;
counting the frequency-multiplied reference clock and recording the edge position of the input signal;
a step of sensing the edge position portion of the input signal in the decomposed multiphase clock and recording a fine edge position; and
calculating a time difference in time of flight between a start signal and a stop signal of the input signal using the edge positions and the fine edge positions.
9. The method of time-to-digital conversion in a lidar system according to claim 8, wherein the edge position and the fine edge position are recorded at each of a rising edge and a falling edge of the input signal.
10. The method of time-to-digital conversion in a lidar system according to claim 8, wherein the step of recording the fine edge position comprises:
a step of decomposing the multiplied reference clock into a first multiphase clock using a first delay locked loop; and
a step of decomposing the decomposed first multiphase clock into a second multiphase clock using a second delay locked loop.
11. The time-to-digital conversion method in a lidar system according to claim 8, wherein the recording of the fine edge positions step senses a recorded edge position portion of the input signal in the decomposed multiphase clock to record a first fine edge position, and senses a recorded first fine edge position portion in a decomposed second multiphase clock to record a second fine edge position.
12. The time-to-digital conversion method in a lidar system according to claim 8, wherein in the step of calculating the time-of-flight difference, a signal intensity of the input signal is confirmed, an object is discriminated using the confirmed signal intensity, and a distance error from the object is corrected using the confirmed signal intensity.
13. The time-to-digital conversion method in a lidar system according to claim 8, wherein in the step of calculating the time-of-flight difference, when the light transmitted to the target object is reflected by the object, noise information corresponding to the reflected light is removed using a pulse width and conversion time information.
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